Disorder in TiO 2─ x

Abstract

We present a theoretical survey, based on reliable computer simulation methods, of defect energetics in TiO 2─ x . A lattice potential for TiO 2 is developed and used in calculations of the formation energies of point and extended defects. We predict vacancies to be the most stable point defects. We show that they will exist in equilibrium with the shear planes that microscopy studies have detected in reduced rutile. We suggest that the stability of the extended defects is due predominantly to the occurrence of large stabilizing relaxations of the cations neighbouring the shear planes. The absence of appreciable binding for point defect clusters may also, however, be important. We show how both factors may be related to the exceptionally high static dielectric constant for the material.